Conventionally, there have been known fluid pressure systems for driving actuators by pneumatic pressure or hydraulic pressure. For example, Patent Literature 1 discloses a fluid pressure system 100 as shown in FIG. 5, in which a bridge circuit is formed between a hydraulic pump 110 and a cylinder 120.
Specifically, in the fluid pressure system 100 shown in FIG. 5, the hydraulic pump 110 and the head side of the cylinder 120 are connected by a first supply line 131, and the hydraulic pump 110 and the rod side of the cylinder 120 are connected by a second supply line 132. The first and second supply lines 131 and 132 are provided with first and second spool valves 141 and 142, respectively. A first tank line 133 branches off from the first supply line 131 at a position between the first spool valve 141 and the cylinder 120. The first tank line 133 is provided with a third spool valve 143. Similarly, a second tank line 134 branches off from the second supply line 132 at a position between the second spool valve 142 and the cylinder 120. The second tank line 134 is provided with a fourth spool valve 144.
The first to fourth spool valves 141 to 144 are solenoid variable throttle valves, and are controlled by a controller 150. The controller 150 transmits electrical signals to the first to fourth spool valves 141 to 144 in accordance with an operating amount of an operating lever 160 operated by an operator.